Technical Abstract:
DSC heating-cooling cycles (0 - 200 deg C) were repeated on PLA/PHEE blends to study the miscibility of the two polymers. The initial DSC thermogram shows two distinguishable Tg's corresponding to the respective neat polymers. The Tg's are accompanied by a crystallization and a melting peak resulting from PLA's deltaHc/Tc and deltaHm/Tm. However, subsequent DSC runs show that the thermogram profiles are dependent on the number of DSC cycles repeated: TgPLA and TgPHEE eventually merge into a single Tg, while deltaHc and deltaHm increase to maximum values then decrease to zero. It is concluded that at the blend's thermo-equilibrium state, reached only after repeated DSC runs, PLA and PHEE are miscible, as indicated by the single Tg. Also, the crystallization of PLA is prevented by the amorphous PHEE. The number of DSC runs needed to reach a single Tg, maximum deltaH and zero deltaH, depends on the blend's composition.